Neisseria lactamica is a harmless coloniser of the infant respiratory tract, and has a mutually-excluding relationship with the pathogen Neisseria meningitidis. Here we report controlled human infection with genomically-defined N. lactamica and subsequent bacterial microevolution during 26 weeks of colonisation. We find that most mutations that occur during nasopharyngeal carriage are transient indels within repetitive tracts of putative phase-variable loci associated with host-microbe interactions (pgl and lgt) and iron acquisition (fetA promotor and hpuA). Recurrent polymorphisms occurred in genes associated with energy metabolism (nuoN, rssA) and the CRISPR-associated cas1. A gene encoding a large hypothetical protein was often mutated in…
African Lakes Cichlids are one of the most impressive example of adaptive radiation. Independently in Lake Victoria, Tanganyika, and Malawi, several hundreds of species arose within the last 10 million to 100,000 years. Whereas most analyses in cichlids focused on nucleotide substitutions across species to investigate the genetic bases of this explosive radiation, to date, no study has investigated the contribution of structural variants (SVs) to speciation events (through a reduction of gene flow) and adaptation to different ecological niches. Here, we annotate and characterize the repertoires and evolutionary potential of different SV classes (deletion, duplication, inversion, insertions and translocations)…
We report the identification of the biosynthetic gene cluster for the unusual antibiotic anthracimycin (atc) from the marine derived producer strain Streptomyces sp. T676 isolated off St. John’s Island, Singapore. The 53?253 bps atc locus includes a trans-acyltransferase (trans-AT) polyketide synthase (PKS), and heterologous expression in Streptomyces coelicolor resulted in anthracimycin production. Analysis of the atc cluster revealed that anthracimycin is likely generated by four PKS gene products AtcC-AtcF without involvement of post-PKS tailoring enzymes, and a biosynthetic pathway is proposed. The availability of the atc cluster provides a basis for investigating the biosynthesis of anthracimycin and its subsequent bioengineering…
Global yields of potato and tomato crops have fallen owing to potato late blight disease, which is caused by Phytophthora infestans. Although most commercial potato varieties are susceptible to blight, many wild potato relatives show variation for resistance and are therefore a potential source of Resistance to P. infestans (Rpi) genes. Resistance breeding has exploited Rpi genes from closely related tuber-bearing potato relatives, but is laborious and slow. Here we report that the wild, diploid non-tuber-bearing Solanum americanum harbors multiple Rpi genes. We combine resistance (R) gene sequence capture (RenSeq) with single-molecule real-time (SMRT) sequencing (SMRT RenSeq) to clone Rpi-amr3i.…
Targeted capture provides an efficient and sensitive means for sequencing specific genomic regions in a high-throughput manner. To date, this method has mostly been used to capture exons from the genome (the exome) using short insert libraries and short-read sequencing technology, enabling the identification of genetic variants or new members of large gene families. Sequencing larger molecules results in the capture of whole genes, including intronic and intergenic sequences that are typically more polymorphic and allow the resolution of the gene structure of homologous genes, which are often clustered together on the chromosome. Here, we describe an improved method for…
Current DNA assembly methods are prone to sequence errors, requiring rigorous quality control (QC) to identify incorrect assemblies or synthesized constructs. Such errors can lead to misinterpretation of phenotypes. Because of this intrinsic problem, routine QC analysis is generally performed on three or more clones using a combination of restriction endonuclease assays, colony PCR, and Sanger sequencing. However, as new automation methods emerge that enable high-throughput assembly, QC using these techniques has become a major bottleneck. Here, we describe a quick and affordable methodology for the QC of synthetic constructs. Our method involves a one-pot digestion-ligation DNA assembly reaction, based…
Many interspecies hybrids have been discovered in yeasts, but most of these hybrids are asexual and can replicate only mitotically. Whole-genome duplication has been proposed as a mechanism by which interspecies hybrids can regain fertility, restoring their ability to perform meiosis and sporulate. Here, we show that this process occurred naturally during the evolution of Zygosaccharomyces parabailii, an interspecies hybrid that was formed by mating between 2 parents that differed by 7% in genome sequence and by many interchromosomal rearrangements. Surprisingly, Z. parabailii has a full sexual cycle and is genetically haploid. It goes through mating-type switching and autodiploidization, followed…
Gene duplication is a major source of genetic variation that has been shown to underpin the evolution of a wide range of adaptive traits [1, 2]. For example, duplication or amplification of genes encoding detoxification enzymes has been shown to play an important role in the evolution of insecticide resistance [3-5]. In this context, gene duplication performs an adaptive function as a result of its effects on gene dosage and not as a source of functional novelty [3, 6-8]. Here, we show that duplication and neofunctionalization of a cytochrome P450, CYP6ER1, led to the evolution of insecticide resistance in the…
Myotonic dystrophy type 1 (DM1) is a multisystem disorder, caused by expansion of a CTG trinucleotide repeat in the 3′-untranslated region of the DMPK gene. The repeat expansion is somatically unstable and tends to increase in length with time, contributing to disease progression. In some individuals, the repeat array is interrupted by variant repeats such as CCG and CGG, stabilising the expansion and often leading to milder symptoms. We have characterised three families, each including one person with variant repeats that had arisen de novo on paternal transmission of the repeat expansion. Two individuals were identified for screening due to…
We investigated genomic diversity of a yeast species that is both an opportunistic pathogen and an important industrial yeast. Under the name Candida krusei, it is responsible for about 2% of yeast infections caused by Candida species in humans. Bloodstream infections with C. krusei are problematic because most isolates are fluconazole-resistant. Under the names Pichia kudriavzevii, Issatchenkia orientalis and Candida glycerinogenes, the same yeast, including genetically modified strains, is used for industrial-scale production of glycerol and succinate. It is also used to make some fermented foods. Here, we sequenced the type strains of C. krusei (CBS573T) and P. kudriavzevii (CBS5147T),…
Carbapenemases are a major concern for the treatment of infectious diseases caused by Gram-negative bacteria. Although plasmids are responsible for the spread of resistance genes among these pathogens, there is limited information on the nature of the mobile genetic elements carrying carbapenemases in Pseudomonas aeruginosa.We combined data from two different next-generation sequencing platforms, Illumina HiSeq2000 and PacBio RSII, to obtain the complete nucleotide sequences of two blaVIM-1-carrying plasmids (pAMBL1 and pAMBL2) isolated from P. aeruginosa clinical isolates.Plasmid pAMBL1 has 26?440 bp and carries a RepA_C family replication protein. pAMBL1 is similar to plasmids pNOR-2000 and pKLC102 from P. aeruginosa and…
Modern sequencing platforms generate enormous quantities of data in ever-decreasing amounts of time. Additionally, techniques such as multiplex sequencing allow one run to contain hundreds of different samples. With such data comes a significant challenge to understand its quality and to understand how the quality and yield are changing across instruments and over time. As well as the desire to understand historical data, sequencing centres often have a duty to provide clear summaries of individual run performance to collaborators or customers. We present StatsDB, an open-source software package for storage and analysis of next generation sequencing run metrics. The system…
The Southern Ocean houses a diverse and productive community of organisms. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis cylindrus, based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. cylindrus genome consists of genetic loci with alleles…
Long-read sequencing can overcome the weaknesses of short reads in the assembly of eukaryotic genomes, however, at present additional scaffolding is needed to achieve chromosome-level assemblies. We generated PacBio long-read data of the genomes of three relatives of the model plant Arabidopsis thaliana and assembled all three genomes into only a few hundred contigs. To improve the contiguities of these assemblies, we generated BioNano Genomics optical mapping and Dovetail Genomics chromosome conformation capture data for genome scaffolding. Despite their technical differences, optical mapping and chromosome conformation capture performed similarly and doubled N50 values. After improving both integration methods, assembly contiguity…
ß-Lactone natural products occur infrequently in nature but possess a variety of potent and valuable biological activities. They are commonly derived from ß-hydroxy-a-amino acids, which are themselves valuable chiral building blocks for chemical synthesis and precursors to numerous important medicines. However, despite a number of excellent synthetic methods for their asymmetric synthesis, few effective enzymatic tools exist for their preparation. Here we report cloning of the biosynthetic gene cluster for the ß-lactone antibiotic obafluorin and delineate its biosynthetic pathway. We identify a nonribosomal peptide synthetase with an unusual domain architecture and an L-threonine:4-nitrophenylacetaldehyde transaldolase responsible for (2S,3R)-2-amino-3-hydroxy-4-(4-nitrophenyl)butanoate biosynthesis. Phylogenetic analysis…